Process for the fluid catalytic cracking of mixed feedstocks of hydrocarbons from different sources

ABSTRACT

A process for the fluid catalytic cracking of mixed hydrocarbon feeds from different sources is described, such as feeds A and B of different crackability, the process being especially directed to obtaining light fractions such as LPG and comprising injecting feed A in the base of the riser reactive section and feed B, of lower crackability, at a height between 10% and 80% of the riser, with feed B comprising between 5% and 50% of the total processed feed. The process requires that the feeds present differences in the contaminant content, improved dispersion of feeds A and B and feed B injection temperature same or higher than that of feed A.

BACKGROUND INFORMATION

Fluid catalytic cracking (FCC) is carried out by contacting hydrocarbonsin a tubular reaction section or riser with a catalyst made up of a fineparticulate material. The most common feedstocks to be submitted to aFCC process are usually those refinery streams from vacuum tower sidecuts named heavy vacuum gasoils (HVGO) or heavier than the latter, fromthe bottom of atmospheric towers, named atmospheric residua (ATR), orstill, admixtures of these streams.

These streams, having densities typically in the range of from 8° to 28°API, in order to deeply alter their composition and convert them tolighter, more valuable hydrocarbon streams, should be submitted to achemical process such as the catalytic cracking process.

During the cracking reaction, substantial amounts of coke, as a reactionby-product, are deposited on the catalyst. Coke is a high molecularstock made up of hydrocarbons that contain of from 4 wt % to 9 wt %hydrogen in their composition.

The coke-recovered catalyst normally designed as “spent catalyst” isdirected to the regenerator. In the regeneration zone, in a regeneratorvessel kept at high temperature, coke deposited on the surface and inthe catalyst pores is burned. Coke withdrawal by combustion leads to thecatalyst activity recovery and releases heat in a sufficient amount toprovide for the thermal requirement of the catalytic cracking reactions.

The fluidization of the catalyst particles by gaseous streams allows thecatalyst transport between the reaction zone and the regeneration zoneand vice-versa. The catalyst, besides doing its essential task ofpromoting the chemical reaction catalysis, is also the heat transportmedium from the regenerator to the reaction zone.

The technique is abundant in descriptions of hydrocarbon crackingprocesses in a stream of fluidized catalyst, with catalyst transportbetween the reaction zone and the regeneration zone, and burning of cokein the regenerator.

In spite of the rather long existence of FCC processes, there is acontinuous search for new techniques for improving the process,increasing the yield in more valuable products, such as gasoline andLPG. Broadly, it may be stated that the main objective of FCC processesis the maximization of said more valuable products.

The maximization of these products is basically obtained in two ways.One is the increase of the so-called “conversion”, corresponding to thereduction in the production of heavy products such as clarified oil andlight cycle oil. Another way is the reduction in the coke and fuel oilyields, that is, through the lower “selectivity” to these products.

The lower production of these two latter products, increasing theprocess selectivity to the target products, has as further beneficialresults the need of smaller air blowers and wet gas compressors, thosebeing big-sized, energy-consuming machines generally limiting of theUFCC capacity. Besides, it is economically interesting to promote therise of more valuable products such as gasoline and LPG.

One important aspect to consider is the interest or need to increase LPGproduction according to the refiner's needs.

The experts know that an important feature of the FCC process is theinitial contact of the catalyst and feed, this having a paramountinfluence on the conversion and selectivity of the process to generatevaluable products. In a FCC process, the pre-heated hydrocarbon feed isinjected near the bottom of a conversion zone or riser, where itcontacts the flux of regenerated catalyst. It is from the regeneratedcatalyst that the feed receives heat in sufficient amount to vaporizeand provide for the thermal demand of the endothermic reactions thatpredominate in the process.

After the riser, a long vertical tube having dimensions in an industrialunit of ca. 0.5 m to 2.0 m diameter by 25 m to 40 m height, where thechemical reactions occur, the spent catalyst, having coke deposited onits surface and pores, is separated from the reaction products. Thespent catalyst is then directed to the regenerator to burn the coke inorder to have its activity restored and generate the heat that, beingtransferred from the catalyst to the riser, will be used by the process.

The conditions existing in the feed injection location of the riser aredetermining as related to the products formed in the reaction. In thisregion the initial mixture of the feed and regenerated catalyst occurs,heating the feed until the boiling point of its constituents is attainedwith the vaporization of most of such constituents. The total residencetime of the hydrocarbons in the riser is around 2 seconds.

In order to process the catalytic cracking reactions, it is requiredthat the feed vaporization in the region of admixture with the catalystoccurs quickly so that the vaporized hydrocarbon molecules may contactthe catalyst particles—the size of which is around 60 microns—permeatingthrough the catalyst micropores and reacting in the acidic sites.Failure in achieving this quick vaporization results in the thermalcracking of the feed liquid fractions.

It is well known that thermal cracking favors the build up ofby-products such as coke and fuel gas, mainly during the cracking ofresidual feeds. Coke poisons the acidic sites and may even blockcatalyst pores. Therefore, thermal cracking in the riser bottomundesirably competes with the catalytic cracking, object of the process.

The optimization of the feed conversion usually requires the maximumcoke removal from the catalyst in the regenerator. Coke combustion maybe obtained in a partial or total combustion regimen.

In the partial combustion regimen, the gases produced by coke combustionare mainly made up of CO₂, CO and H₂O and the coke content in theregenerated catalyst is of the order of 0.1 wt % to 0.3 wt %. In thetotal combustion regimen, to be carried out in the presence of largeroxygen excess, practically all the CO produced in the reaction isconverted to CO₂.

The oxidation reaction of CO to CO₂ is highly exothermic, making totalcombustion to occur with a large heat release, resulting in highregeneration temperatures. However, total combustion leads to a catalysthaving less than 0.1 wt % and preferably, less than 0.05 wt % coke, thisbeing a favorable feature relative to the partial combustion, besidesavoiding the need of a costly boiler for further CO combustion.

The coke increase on the spent catalyst causes an increase of the cokeburned in the regenerator by mass unit of the circulated catalyst. Inconventional FCC units heat is removed from the regenerator in thecombustion gas and mainly in the hot regenerated catalyst stream. Anincrease in the coke content on the spent catalyst increases thetemperature of the regenerated catalyst as well as the temperaturedifference between the regenerator and the reactor.

Therefore a decrease in the regenerated catalyst flow rate to thereactor, normally designated as catalyst circulation rate, is requiredin order to attend to the reactor thermal demand and keep the samereaction temperature. However, the lower catalyst circulation raterequired by the larger temperature difference between the regeneratorand the reactor leads to a lower catalyst/oil ratio, this in turnreducing conversion.

Thus, catalyst circulation from the regenerator to the reactor isascertained by the riser thermal demand as well as by the regeneratortemperature, which is a function of coke production. Since the catalystcirculation itself affects coke produced in the riser, it is concludedthat the catalytic cracking process works under a thermal balanceregimen. In view of the preceding, operation at high regenerationtemperatures is to be avoided.

Generally, on using modern FCC catalysts, regenerator temperatures andtherefore regenerated catalyst temperatures are kept below 760° C.,preferably below 732° C., since activity loss would be severe above thisfigure. A desirable operation range is of from 685° C. to 710° C. Thelower limit is dictated mainly by the need to secure suitable cokecombustion.

On processing increasingly heavy feeds, there is a tendency to increasecoke production and the operation under total combustion requires theuse of catalyst coolers to keep the regenerator temperature withinacceptable limits. Generally, catalyst coolers remove heat from aregenerator catalyst stream, and return to said vessel a substantiallycooled catalyst stream.

As for the fluid-dynamic features of the riser, where the catalyticcracking reactions of the invention occur, it is well known thatcatalyst solid particles are entrained in the reaction medium duringcontact with the feed and other vaporized materials.

This kind of reactor is normally of tubular shape where, in order toreduce by-products, operation should be carried out according to ahydrodynamic flow regimen, so that the superficial gas velocity is highenough to cause that catalyst flux is in the same direction as that ofthe feed and of other gases present therein. That is, the liquid andvaporized feed entrains the catalyst particles throughout the entirepath in the tubular reactor.

These flow regimens are known by the experts as fast fluidized bed,riser regimen or more generally as transport regimen, those regimensbeing the preferred ones when one deals with reaction systems thatrequire continuous flow reactors.

Generally, for a certain cross section area of a tubular reactor, whichis a function of the reactor diameter, the catalyst concentration, in afluidized bed reactor, is reduced as a result of increased superficialgas velocity. The higher the superficial gas velocity, the higher willbe the reactor lengths required to allow that a certain amount of feedmay contact the required amount of catalyst. Those higher superficialgas velocities require a higher L/D (Length/Diameter) ratio or aspectratio of the reactor, which is the ratio between the reactor length andits diameter.

In the patent literature several publications suggest the multipleinjection of the same feed in FCC units.

U.S. Pat. No. 3,246,960 teaches an FCC apparatus built so that theinjection of the same feed in different locations of the riser iscarried out so as to promote a more uniform mixture between feed andcatalyst, with the consequent increase in gasoline octane rating.

International publication WO 0100750A1 teaches the re-cracking ofnaphtha to increase LPG yield, simultaneously with the split-feedinjection of the same feed. The split-feed is injected in at least twodifferent locations above the reactor lower position. The process aimsat maximizing diesel oil production.

U.S. Pat. No. 4,869,807 teaches a process for converting anon-segregated hydrocarbon feed in a FCC reactor in the presence of azeolitic catalyst for producing gasoline. The same feed is divided inportions and injected into a plurality of locations along the length ofthe FCC reactor, with of from 60 to 75% by volume being injected in thelowest injection position. The distance between this location and theimmediately superior location comprises at least 20% of the totalreactor length. Multiple injection would allow increased gasoline octanerating.

U.S. Pat. No. 5,616,237 teaches the same technique of multiple injectionof the same feed in different locations to secure selectivityimprovements. This approach reduces the contact time of the feed, withthe consequent bottom conversion. It is also suggested to promote arecycle of the non converted friction to several injection locationsalong the riser length.

U.S. Pat. No. 6,416,656 discloses a process for catalytically crackinghydrocarbon stocks in a riser or fluidized bed reactor to increasesimultaneously the yields of diesel and liquefied gas. The processincludes the steps of: first, charging a gasoline stock and a catalyticcracking catalyst into a lower zone of the reactor to permit contactbetween the catalyst and the gasoline stock and to produce a liquefiedgas-rich oil-gas mixture containing reacted catalyst. The resultingliquefied gas-rich oil-gas mixture (still containing reacted catalyst)is then introduced into a reaction zone above the lower zone of thereactor. Simultaneously, at least one conventional catalytic crackinghydrocarbon feed is also fed independently into at least two sitessituated at different heights above the lower zone of the reactor. Theresulting mixture is then separated in a conventional fashion.

Another approach from the patent literature involves injecting anauxiliary stream such as water or petroleum fractions in a locationdownstream of the injection of the feed to be cracked in order topromote an increase in the mixing temperature in the area of the feedinjection. This is done aiming at increasing the vaporized percent ofresidual feeds, without altering the riser outlet temperature.

Such an approach is taught in U.S. Pat. No. 4,818,372 that relates to aFCC apparatus with temperature control including an upflow or downflowreactor, a device to introduce the hydrocarbon feed under pressure andin contact with a regenerated cracking catalyst. The FCC apparatuscomprises further at least a device for injecting an auxiliary fluiddownstream of the reactor zone where feed meets the catalyst, whereby itis desired to attain a higher temperature in the mixing zone of feed andcatalyst. This document does not contemplate feed segregation, rather,it makes use of an inert, external fluid the main effect of which is thecooling of the injection region of said fluid, with temperature controland increase in catalyst circulation rate. In this respect please seeExample 1, column 7, lines 55 to 60 of said patent, where it is definedthat the feed is the same feed, injected once in the riser base whilethe other injection is effected with a cooling fluid as water or eithera product of the cracking itself. The proposed process is directed tothe cracking of a residual feed, the main feature of which is to containat least 10% of a fraction having boiling point higher than 500° C. Thedesired goal when increasing the mixture temperature is to secure thevaporization of heavier fractions, while at the same time promoting athermal shock on said fractions, aiming initially at converting thebigger molecules into lighter compounds, able to vaporize andcatalytically cracking in a further step.

This is attained by injecting an auxiliary fluid above the feedinjection location, from which the cracking reactions occur under milderconditions, at constant reaction temperature and independently of thedesired mixing temperature.

The goal of the present invention is different and directed to thesituation where feeds of different crackability are processed at thesame time in one single riser. Under these conditions, it is suggestedto inject the feed of lower crackability, the coke selectivity of whichas well as the contaminant concentration is higher, in a riserdownstream injection location. This aims at increasing the severity ofthe reactions of the feed of better quality injected in the beginning ofthe reactive section of the riser aiming mainly at higher LPG yields.This is obtained by a localized increase in the regenerated catalystcirculation as well as of the temperature of the riser section comprisedbetween the two injections. Further, regenerated catalyst that contactsthe better quality feed in the beginning of the riser reactive sectionis less deactivated by virtue of the local absence of contaminants aswell as the higher coke production caused by the lower crackabilityfeed.

The injection location of the feed of lower crackability in the riser ischosen so as to maximize LPG production, and is a function of theproperties of the different feeds to be processed, as well as of theriser outlet reaction temperature.

A further distinguishing point between the present invention and U.S.Pat. No. 4,818,372 is that in this latter the total catalyst circulationis substantially increased. This may be observed from Example 1, in theTable of column 8, which sets forth an increase in the catalystcirculation rate from 4.6 to 6.7 by injecting a certain flow rate ofwater in the middle location of the riser. As a consequence, more cokewill be formed, overloading the air blower of the regeneration sectionthat normally is already very tight in terms of accepting any cokeincrease.

In the present invention, the resulting rise in catalyst circulationrate is only local, being limited to the section comprised between thelower and upper injections, but there is no significant increase intotal catalyst circulation rate. Actually, as the lower crackabilityfeed and normally having higher coke selectivity, is processed in theriser under milder temperature and contact time conditions, it is to beexpected coke production to be slightly reduced.

Further, in the downstream injection location, the catalyst is recoveredby a considerable content of deposited coke, this making it lessselective to further coke formation. This way no overburden is expectedon the air blower of the regeneration section, instead, a relief is tobe expected.

A further disadvantage of the teachings of said U.S. Pat. No. 4,818,372is the overburden of the riser, reactor cyclones, transfer line, mainfractionator as well as of the top condensers of the fractioning sectionat the moment of the injection of make up water in the riser. This leadsto adapt the dimensioning of most of the equipment to the requirement ofthe claimed process.

Besides, injecting water in the riser means a poor energetic balance ofthe FCC process, since all the energy that water removes from theconverter is lost when the same water condenses on the top of the mainfractionator coolers. It should also be mentioned the furtherdisadvantage of additional acidic water generation in the refinery.

As taught in U.S. Pat. No. 4,818,372, the segregated injection of anexternal stream in a downstream riser location is carried out aiming atcontrolling the riser temperature profile. This makes possible to keepthe upstream section of the riser at a relatively higher temperaturewithout altering the riser top temperature or TRX (reactiontemperature). Such control may also be carried out through a heavynaphtha recycle, as taught in U.S. Pat. No. 5,087,349.

Aiming at the same goal, U.S. Pat. No. 5,389,232 teaches a heavy naphtharecycle in downstream riser locations.

Aiming at minimizing naphtha overcracking reactions, U.S. Pat. No.4,764,268 suggests the injection of a LCO stream in the top of theriser.

A similar alternative, taught in U.S. Pat. No. 5,954,942 aims atincreasing conversion, through a quench or quick cooling with the aid ofa steam auxiliary stream in the riser upper region.

International publication WO 93/22400 mentions the possibility ofinjecting along the riser a cracking product such as LCO aiming atcooling the riser and consequently promoting an increase in the catalystcirculation rate so as to make possible improved performance of ZSM-5additives.

Contrary to U.S. Pat. Nos. 4,818,372, 4,764,268, 5,389,232, 5,954,942and International publication WO 93/22400, in the present invention thefeed injected in the one or more downstream riser locations is not anauxiliary external stream but rather one of the streams that normallymake up the feed of the FCC unit. Since the segregated feed is injectedat a temperature equal or higher than the feed temperature, the improvedyields should not be considered as caused by an increase in the totalcatalyst circulation rate.

As regards the injection of the segregated feed in different locationsof the riser, some publications suggest to differentiate feeds as afunction of the nitrogen content only.

Thus, U.S. Pat. No. 4,985,133, aiming at reducing NO_(x) release intothe regenerator, teaches an alternative for the injection of the highertotal nitrogen feed in the riser base, the less contaminated feed beinginjected in a higher nozzle.

U.S. Pat. No. 4,218,306 teaches a FCC process for producing gasoline anddistillate by combining cracking of a distillation gasoil injected inthe base of a cracking zone of a riser for admixture with a regeneratedcatalyst to form a catalyst suspension at high temperature. A secondhydrocarbon fraction having more difficult cracking features is chargedat a location 3.05 m to 9.14 m (10 to 30 feet) downstream the firstinjection. The riser outlet temperature is limited to the range between482° C.-593° C. (900° F. to 1100° F.), preferably 510° C.-530° C. (950°F. to 985° F.).

Said U.S. Pat. No. 4,218,306 is directed to improved gasoline yields, asset forth in the main claim. In a patentably distinguishing way, thepresent invention is a much more flexible process, directed to eitherLPG only or to the sum LPG+gasoline, according to the injection locationof the feeds in the riser as well as the desired riser outlettemperature. Besides, contrary to the teachings of said US patent,according to the invention, the injection of the lower crackability feedis not limited to the riser section placed 10 to 30 feet (correspondingto 6% to 30% of the reactive section of a typical industrial riser)downstream of the riser base injection of the better crackability feed.

In the present invention the injection location of the lowercrackability feed is set forth aiming at obtaining the maximum possibleLPG yield. Such location is a function of the properties of the feeds ofdifferent sources to be processed, of the percent of the lowercrackability feed processed based on the total feed flow rate as well asof the riser outlet reaction temperature. Said injection location may bepositioned at any location downstream the injection of the lower feed,but preferably of from 10% to 80% of the riser reactive section. As ageneral rule, the ideal location for injecting the lower crackabilityfeed is that, which provides for the operation conditions favoring themaximization of LPG production in the section between the two feedinjections. Further, said location should conform to the minimumresidence time required by the lower crackability feed to undergo thedesired conversion to lighter products, including LPG.

It should be noted that in column 4, line 3 of U.S. Pat. No. 4,218,306,it is stressed that the downstream injection should be submitted to veryslight or no heating at all, this featuring a feed cooling or quenching,such cooling being completely absent from the inventive process.Therefore, the concept of the said US patent, as applied to the mainobjective of the present invention, that is, maximum LPG productionwould not lead to the desired results.

U.S. Pat. No. 6,123,832 teaches a FCC process for the conversion ofhydrocarbon mixtures based on a non-linear phenomenon consisting in thefact that the lower yield in valuable products is not linearly reduced,neither the coke yield increases linearly, with the increase in heavycomponent in the FCC feed.

This means that the marginal deleterious effect caused by feedcontaminants on the FCC catalyst is weaker with the increase in heavycomponents. Alpha and beta different quality feeds are to be injected indifferent nozzles. Alternatively, different nozzles may be used. Stillalternatively, the riser is divided in two zones for separate crackingin one portion of the riser. Thus, the benefit of using at least onehigh CCR feed stems from the fact that the lower CCR feed increasesconversion to a much higher degree than the conversion loss due to thehigher CCR content feed.

The conditions for differentiating alpha- and beta-feeds are: a) the CCRfigures differ from at least 2 points in wt %; or b) they differ inhydrogen content by at least 0.2 wt %; or c) they differ in API gravityby at least two points; or d) they differ in nitrogen content by atleast 50 ppm; or e) they differ in the C/H ratio by at least 0.3; or f)they differ in average boiling point by at least 93.3° C. (200° F.). Thetechnique taught in said US patent is not clear as regards which feed isto be injected in which nozzle or riser position, or in which riser. Oneclaim is directed to the methodology for calculating possible feedmixtures that could lead to desirable results in terms of valuableproducts. Injection is non-linear (claim 2, column 9).

Another alternative is the injection of an external stream such as analcohol, ether or a gasoil of better quality than the feed injected inthe riser base, as taught in U.S. Pat. No. 5,271,826. This approach doesnot contemplate feed segregation according to the concept of theinvention.

Another approach for feed segregation, as taught in U.S. Pat. No.4,422,925 and U.S. Pat. No. 3,617,497 is based on the difference betweenfeeds exclusively focused on molecular weight, while suggesting multipleinjections in the riser. The lower molecular weight feed is injected inthe riser base aiming at maximizing gasoline yields. However, as will beseen hereinafter in the present specification, a single parameter fordifferentiating feeds is not sufficient for obtaining the desiredresults in terms of yields and products.

On the other hand, it is well known that the density is closelyassociated to the extent of feed contamination, as reported on page 132of the article by M. A. Torem et al., in “Development of a newcoefficient to predict FCC feedstock cracking”, ACS 206th NationalMeeting—Advances in Fluid Catalytic Cracking—1993, Chicago, USA.

The considerations set forth above indicate that, in spite of theextended literature and patent publications, there is no description norsuggestion, In isolated or combined way, of a FCC process free ofoverall sensible cooling effect and without significant alteration ofthe total catalyst circulation rate, having improved conversion to lightproducts such as LPG and gasoline, this being obtained from a mixed Aand B hydrocarbon feed where feed B is produced by a thermal process orby physical separation, is more selective to coke formation relative tothe feed to be injected in the base of the riser reactive section, ismore refractory to cracking and is more heavily contaminated, where theconditions for injecting the segregated feed involve suitable distancesbetween the injection locations in the riser and optimized dispersion ofboth feeds A and B aiming at maximizing LPG production, such processbeing described and claimed in the present application.

SUMMARY OF THE INVENTION

Broadly, the process of the invention for the fluid catalytic crackingof mixed A and B feeds of hydrocarbons of different sources in a riserreactor in the presence of a zeolite catalyst under cracking conditionsand in the absence of added hydrogen, for obtaining mainly lightproducts such as LPG, feed B being more refractory to cracking,comprises the segregated injection of such A and B feeds in distinctriser locations, and wherein:

-   -   a) feed B is in an amount of from 5% and 50% by mass based on        the total processed feed;    -   b) the injection location of feed A sets the base of the riser        reactive section;    -   c) feed B is injected in one or more riser locations downstream        the injection location of feed A and shows, in combination:    -   i) higher coke selectivity relative to feed A; and    -   ii) higher contaminant content,        and where the injection conditions of feed B involve:

-   i) injection location between 10% and 80% of the total length of the    riser reactive section;

-   ii) improved dispersion; and

-   iii) same or higher injection temperature based on the injection    temperature of feed A,    said process resulting in recovering LPG in a higher amount than    would be possible if feeds A and B were injected both in the base of    the riser reactive section.

Thus the present invention provides a FCC process for the cracking ofmixed hydrocarbon feeds of different crackability having increasedconversion to valuable products such as the sum of LPG and gasolineresulting from modifying the riser temperature profile.

The present invention provides further a FCC process for the cracking ofmixed hydrocarbon feeds of different crackability where the modificationof the riser temperature profile is obtained from the injection of aless crackable feed under optimized temperature and dispersionconditions, at a length of from 10% to 80% of the base of the riserreactive section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 attached is a graph of the temperature profile of a FCC riserwhere the mixed hydrocarbon feed A and B is cracked according to theinvention. Illustrated are locations that represent respectively theinjection of feed B at 25% of the riser reactive section and 50% of theriser reactive section.

FIG. 2 attached is a graph of conversion vs. coke, where the full linestands for the base case and the dotted line, for the invention.

FIG. 3 attached is a graph of LPG vs coke, where the full line standsfor the base case and the dotted line, for the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates therefore to a FCC process for theconversion of mixed hydrocarbon feeds of different sources having highyields in valuable products, mainly LPG, the increased conversionresulting from the segregated injection of the different feeds to beprocessed according to the crackability features as well as from thepresence of contaminants in each feed.

The invention is applicable to FCC units specially directed to theprocessing of mixed feeds from different refining processes, forexample, the straight-run distillation gasoil and more refractory feeds,from thermal processes or physical separation.

One aspect of the invention is therefore a FCC process for theconversion of mixed hydrocarbon feeds where the improved processprofitability results from the injection of each of the feeds indifferent riser locations.

The process may be applied to FCC units that comprise tubular riserreactors as well as those that comprise downflow reactors.

The catalyst used in the performance of the inventive process ispreferably a catalyst that comprises a high activity crackingcrystalline zeolite as well as a fluidizable particle size. A preferredcatalyst comprises a Y zeolite. Another preferred catalyst comprises aZSM-5 zeolite. Still useful for the purposes of the invention is thecombined use of catalysts that comprise said Y and ZSM-5 zeolites, inany amount. As is known by the experts, this zeolite class favors theLPG production. The zeolite or zeolites may be present also asadditives.

As a general rule, the residence time for the contact of the hydrocarbonfeed with the catalyst is in the range of from 0.5 to 10 seconds ormore, preferably, of from 1 to 2 seconds.

And the residence time of feed A in the riser submitted to the crackingcatalytic reactions, measured between feed A and feed B injections, isin the range of from 0.5 and 2 seconds.

The catalyst/oil ratios are between 2/1 to 15/1, preferably of from 6/1to 8/1.

Residence times are determined so that feed A is allowed longer contacttime with the catalyst suspension and a huge amount of gasoline and LPGis obtained, mainly LPG, while at the same time the required period forthe cracking of B feed is obeyed. Imparting a high dispersion degree tofeed B may reduce such period of time.

As in typical catalytic cracking processes, the present process involvesthe contact of the hydrocarbon feed with a solid particulate catalyst ina reaction zone under conditions such that the hydrocarbon feed isconverted into desired, lower molecular products accompanied by theproduction of hydrogen and other gaseous products and coke deposition onthe surface of the catalyst particles. Such systems comprise a transportzone, through which cross vaporized hydrocarbons and solid catalystsuspended in or carried by hydrocarbon vapors, optionally combined withsteam.

Reaction products and catalyst are discharged from the transport zone toa separation zone in which hydrocarbon vapors are separated fromcatalyst.

Due to coke deposition on the catalyst surface the catalyst is partiallydeactivated during the passage through the reaction zone. The partiallydeactivated catalyst is designed as spent catalyst in opposition to theregenerated catalyst. Spent catalyst is regenerated by combustion ofcoke deposits on its surface by means of an oxygenated gas.

Regeneration of spent cracking catalyst is carried out after theseparation of spent catalyst from reaction products discharged from thereaction zone. At first spent catalyst is made to contact in a strippingzone, a stripping medium, normally steam, to withdraw vaporizableentrained and occluded hydrocarbons from the catalyst.

From the stripping zone, the stripped catalyst is directed to aregeneration zone where the stripped spent catalyst is regenerated byburning coke deposits on same with the aid of an oxygenated gas,normally air.

The hot regenerated catalyst resulting from the regeneration zone isthen recycled to the reaction zone to be contacted with a furtherhydrocarbon feed.

The inventive process results in increased profits for FCC units thatprocess mixed feeds.

For a feed or mixed stream generally designed as feed A and feed B, feedA is a gasoil-type feed, having more favorable crackability features,such as a vacuum distillation heavy gasoil (HVGO).

And feed B is a stream normally produced from a thermal or physicalseparation process, such as for example thermal cracking, pyrolysis,delayed coking, shale oil retorting, etc. Generally, feed B contains ahigh degree of total nitrogen, basic nitrogen and/or sulfur compounds.Polynuclear aromatic compounds may equally be present, therefore havinga trend to form coke, besides metal contaminants such as nickel, harmfulto the cracking catalysts.

Feed B may be a single stream or be a mixture of streams from thermal orphysical separation processes.

The stream or mixture of streams from thermal or physical separationprocesses, normally more refractory to cracking than the vacuumdistillation gasoil (HVGO)—the usual FCC unit feed—is injected in one ormore locations downstream the main injection directed to the base of theriser reactive section, such locations being placed between 10% and 80%of the riser height.

Alternatively, the injection of feed B is effected in more than oneriser downstream location, as desired by the refiner. Stillalternatively, different B and C feeds may be injected in differentdownstream riser locations.

The amount of feed B relative to feed A varies between 5% and 50% massbased on the total processed feed.

The injection of feed B in a location downstream of feed A injectionprovides to said feed localized conditions of catalytic cracking thatare more severe as regards temperature and catalyst circulation, whileat the same time the regenerated catalyst deactivation caused by coke orcontaminants is minimized.

The combination of the above conditions leads to the maximization of LPGproduction from feed A, without significantly increasing the totalcatalyst circulation nor altering the outlet riser reaction temperature.As a consequence, there are no restrictions to the regeneration sectionair blower, nor are there restrictions regarding the metallurgical limitof the equipment that are downstream of the riser.

On the other hand, the injection location of feed B should be such that,at the same time that it maximizes LPG production from feed A, itprovides reaction conditions (temperature and residence time) sufficientfor obtaining an acceptable LPG yield from the cracking of feed Bitself. Thus, the ideal injection location for injecting feed B dependson the properties of feeds A and B, on the percentage of feed B relativeto the total processed feed and on the riser outlet reactiontemperature.

As for the system for controlling the injection of feed B in the riser,such system can be completely independent from the variables of the FCCconverter.

Alternatively, the control system may be set as a function of thedesired mixing temperature in the contact region of feed A with theregenerated catalyst.

Still alternatively, the control system is set as a function of theobtained LPG yield.

Still alternatively, the control system is a function of any othervariable that it is desired to control, any known control logic beingused for such purpose.

The temperature rise in the mixing region between feed A and theregenerated catalyst is of from 10° C. to 50° C., this being providedfor by injecting feed B at a riser location above the injection of feedA. Such temperature is in the range of from 520° C. to 650° C.

The maximum temperature of feed B is limited to 430° C.

Broadly, it is possible to state that, aiming at obtaining maximum LPGyield, the following assumptions hold:

-   -   i) the lower the crackability of feed B, the longer the period        of time required for it to obtain acceptable conversion levels;    -   ii) the higher the percentage of feed B relative to the total        processed feed, the higher the severity required for the        cracking of feed A;    -   iii) the farther the injection location of feed B relative to        the injection of feed A, the longer the period of time during        which feed A will be submitted to the more severe cracking        conditions that favor LPG yields;    -   iv) the higher the riser outlet reaction temperature, the higher        will be the temperature at which feed A will be submitted to        catalytic cracking.

Usually, temperature increase is accompanied by higher gasoline and LPGyields. However, from a certain temperature, normally situated between540° C. and 560° C., depending on the residence time, gasolineovercracks to LPG, with a substantial increase in LPG yield at theexpense of the gasoline amount to be obtained.

FIG. 2 illustrates the LPG rise obtained as compared to the base case.Data for FIG. 2 were obtained by injecting feed B in an amount of 15 wt% based on the total processed feed. Feed B was injected at a location25% of the riser reactive section, the injection temperature being 80°C. higher than the injection temperature of feed A.

FIG. 3 illustrates, for the same experimental conditions used in FIG. 2,the conversion rise obtained by applying the inventive process.

The higher the severity required for the catalytic cracking of feed A,that is, the higher the cracking temperature, the residence time and thelocal circulation of regenerated catalyst, the higher will be the LPGyield obtained from feed A.

According to the invention, the riser outlet reaction temperature is inthe range of from 520° C. to 590° C.

Besides the maximization of valuable products, the catalytic path, asstressed by the present invention, provides a gasoline product not onlyof octane rating similar to that of the base case, but also of stablequality. Specifically as concerns the quality, it is essential that feedB presents the required cracking conditions, aiming at securing thatgasoline and LCO products do not contain contaminants above the acceptedlevels. There should be enough reaction time for the cracking of feed B,so as to secure that most of the contaminants present in said feed areconveyed to the coke formed on the spent catalyst, instead of beingreleased together with the cracking products. This is an additionalconcern that should be considered in defining the injection location offeed B in the riser. Broadly, such location should not surpass 80% ofthe riser reactive section.

In order to obtain the desired results from the process, feed A as wellas feed B injected in the one or more downstream locations in the risershould be submitted to optimized atomization (dispersion) conditions.Such conditions involve, for example, the use of high-efficiencyfeed-dispersion devices, besides an optimum dispersing fluid/oil ratio,injection temperature or a combination of these conditions.

A high-efficiency feed-dispersion device useful in the inventive processis that one taught in International Application WO 0144406, of theApplicant. However, other commercial feed-dispersion devices can beused, provided they provide optimized conditions for the feed that is tobe dispersed.

The concept of the present invention comprises a temperature rise in theriser section situated between the injection location of feed A in thebase of the riser reactive section and the downstream injection locationof feed B in the riser. As a consequence, there is a high conversionlevel for feed A that favors the total yield of LPG and gasoline byweight.

This is because, contrary to the base case where feeds A and B arecracked in admixture, the initial cracking of feed A separately and atleast 5% by weight of feed B injected in one or more downstream riserlocations cause a temperature rise as well as a higher local catalystcirculation in the riser section situated between the conventionalinjection location and the injection location(s) of feed B.

In the next section, situated between the downstream injection locationand the riser top, more refractory feed B from a thermal or physicalseparation process undergoes thermal and catalytic cracking reactions.Since coked catalyst is less coke sensitive, these reactions occurwithout significant increase in the coke content deposited on thecatalyst.

The position of one or more downstream locations in the riser should beselected so that the reduced contact time can be partially compensatedby optimizing the atomization condition of feed B from thermal orphysical separation process.

It should be understood that, contrary to what is taught instate-of-the-art documents, in the present invention the feed portioninjected in the one or more downstream locations relative to the riserbase does not aim at promoting a quenching, neither controlling thetemperature of the location downstream the injection location.

Besides, the benefits attained by applying the teachings of the presentinvention are not related to a catalyst circulation rate increase, sincethe segregated fraction is not an external stream. This makes possiblethat such stream may assume temperature levels that are the same ordifferent from those of the feed injected in the base of the riserreactive section, as will be discussed in one of the Exampleshereinbelow.

In the present invention, the more refractory stream, from thermal orphysical separation process, feed B, should always be injected in one ofthe downstream locations, while feed A of better crackability should beinjected in a location in the base of the riser reactive section. Thisprocedure allows that feed A of better crackability contacts a moreactive, less contaminated catalyst suspension in the section situatedbetween the base of the riser reactive section and the segregatedinjection of feed B, attaining increased conversion of such feed A.

The fraction of feed B from thermal or physical separation process basedon the total processed feed should be of from 5% to 50% by mass,preferably of from 15% to 25% by mass.

The injection of feeds A and B of different origins in the base of theriser reactive section and in the riser downstream location should besimultaneous.

Still, the best profitability of the inventive FCC process results froma combination of conditions, and not only from one or another isolatedcondition, as taught in some state-of-the-art publications.

Thus, Research carried out by the Applicant has indicated that feed B tobe injected in one or more downstream riser location should have ahigher basic nitrogen and contaminant content, besides specificinjection temperature conditions as well as optimized dispersion. Ascited hereinbefore, U.S. Pat. No. 4,985,133 teaches a single criteriumfor making the difference between the feeds, that is, the highernitrogen content of the feed to be injected in the base of the riserreactive section. On the other hand, U.S. Pat. No. 4,422,925 teaches tomake the difference between feeds by the molecular weight only.

The invention will now be illustrated by the following Examples, whichshould not be construed as limiting it.

EXAMPLES

Aiming at effectively demonstrating the efficacy of the invention, aseries of tests were run in a multipurpose FCC unit owned by theApplicant, such unit having an output of nearly 200 kg/h feed.

The feed characterization is listed in Table 1 below.

Feed A is a direct distillation vacuum gasoil (HVGO) while feed B is aheavy gasoil from a delayed coking unit. TABLE 1 Properties Feed A FeedB Density @ 20/4° C. (g.cm⁻³) 0.9410 0.9486 Viscosity (cSt) @ 82.2° C.132.5 61.4 Total S (ppm) 6,400 5,385 Total N (ppm) 2,880 5,222 Flashpoint, ° C. 168 114

Example 1

Example 1 shows the effect of the injection location. Collected data,listed in Tables 2A and 2B below, evidence the conversion rise tovaluable products by segregating feed B to a location downstream to theconventional feed injection. Case 1 is the base case, where the feedsare injected in admixture in the base of the riser reactive section, inthe amount of 85% heavy vacuum gasoil (HVGO), feed A, and 15% of cokeheavy gasoil (KHGO), feed B. Reaction temperature level (TRX) is 540° C.for all tests.

According to cases 2 and 3 of Tables 2A and 2B, which illustrate theconcept of the invention, the downstream injection location favorsgasoline overcracking, since a rise in LPG is observed at the expense ofgasoline. This difference is explained by the change in the temperatureprofile throughout the riser, as illustrated in FIG. 1. TABLE 2A Feed AFeed B Riser Riser 25% 50% Base Base” Riser Riser Temp. Dispersion steamCase (%) (%) (%) (%) (° C.) (%) 1 85 15 — — 220 — 2 85 — 15 — 220 10 385 — — 15 220 10

TABLE 2B Yields Conv, FG LPG GLN LCO DO Coke Case CTO (%) (%) (%) (%)(%) (%) (%) 1 6.5 66.8 2.8 10.7 48.3 17.0 16.2 5.0 2 6.6 67.8 3.0 12.547.3 17.2 15.0 5.1 3 6.4 68.4 3.2 14.1 45.9 16.5 15.0 5.2Where: CTO = Catalyst To Oil ratio”FG = Fuel GasGLN = GasolineLCO = Light Cycle OilDO = Deasphalted OilLPG = Liquefied Petroleum Gas

Therefore, data indicate a rise in LPG production consequent to i) theincrease in the distance of the downstream injection location relativeto the injection location in the base of the riser reactive section andii) the use of dispersion steam to optimize the dispersion of the feedof lower crackability.

As indicated in the corresponding column of Table 2B, the catalyst tooil ratio CTO practically does not vary, this being a patentablydistinguishing feature of the present invention.

FIG. 1 is a plot of the temperature profile along the riser. This plotillustrates the fact that when the segregated injection is effected in adownward location, a larger section of the riser operates at highertemperatures, which entails a conversion rise for feed A.

Example 2

Data for Example 2, listed in Tables 3A and 3B below, evidence therelevance of optimizing the dispersion conditions of the downwardinjection location.

In all cases, reaction temperature level was 540° C. Data show that anincrease in dispersion steam from 5% to 20% as well as a temperaturerise cause better dispersion with a consequent conversion increase. Thehigher the oil temperature, the lower its viscosity, and consequentlythe lower the diameters of the formed droplets in the atomizationprocess. As a consequence, the more intimate is the contact of oil andcatalyst, which accelerates oil vaporization, the higher the effect ofminimizing thermal cracking reactions, so as to intensify the catalyticroute. Depending to the quality of feed B, according to the one used inExample 2, a temperature rise applied to such feed can be conclusive forthe improvement in the distribution of obtained yields.

Thus, case 7 evidences that in the present invention the benefits areobtained not as a function of a quenching with the consequent increasein catalyst circulation rate, since the catalyst to oil ratio did notvary beyond 0.5 in the studied cases. TABLE 3 A Feed A Feed B base Base25% 50% Riser Riser Riser Riser Temp. Dispersion steam Case (%) (%) (%)(%) (° C.) (%) 4 85 — 15 — 220 5 5 85 — 15 — 220 10 6 85 — 15 — 220 20 785 — 15 — 300 10

TABLE 3B Yields Conv. FG LPG GLN LCO DO Coke Case CTO (%) (%) (%) (%)(%) (%) (%) 4 6.3 67.9 3.0 11.9 48.1 16.6 15.5 4.9 5 6.6 67.8 3.0 12.547.3 17.2 15.0 5.1 6 6.8 68.4 3.0 12.5 47.7 17.1 14.6 5.2 7 6.3 69.6 2.813.5 47.8 16.7 13.7 5.4Where: CTO = Catalyst To Oil ratio”FG = Fuel GasGLN = GasolineLCO = Light Cycle OilDO = Deasphalted OilLPG = Liquefied Petroleum Gas

Example 3

Example 3 illustrates the effect of partial segregation of one of thefeeds, showing that the process of the invention is not applicable whenin spite of different crackability between the feed injected in theconventional nozzle and the feed injected in downstream nozzles, afraction of feed B is injected with feed A in the base of the riserreactive section.

Results for case 9 are inferior to those of base case 8 where the feedis not segregated. Data are collected in Tables 4A and 4B below. In allcases the temperature was kept at 540° C. Thus, in spite of the effectof the temperature profile in the reaction zone, the improvementattained by the concept of segregation of feeds of differentcrackability may be lost when a portion of feed B contaminates feed A inthe base of the riser reactive section. TABLE 4A Feed A Feed B RiserRiser 25% 50% Base “ Base Riser Riser Temp. Dispersion steam Case (%)(%) (%) (%) (° C.) (%) 8 75 25 — — 220 10 9 75 10 15 — 220 10

TABLE 4B Yields Conv. FG LPG GLN LCO DO Coke Case CTO (%) (%) (%) (%)(%) (%) (%) 8 6.7 65.2 3.0 13.2 43.7 17.7 17.1 5.3 9 6.0 64.4 3.1 10.7452 18.2 17.5 5.4Wherein: CTO = Catalyst To Oil ratio”FG = Fuel GasGLN = GasolineLCO = Light Cycle OilDO = Deasphalted OilLPG = Liquefied Petroleum Gas

Example 4

This Example illustrates that, contrary to state-of-the-art processesthat teach improvements in octane rating of the produced gasoline, thepresent process yields a gasoline that does not necessarily undergo anychange in octane rating, the most relevant parameters being keptpractically constant. This behavior is illustrated in Table 5 below.TABLE 5 % % feed % feed feed B A B 50% S_(naphtha) S_(LCO) S_(residuum)Case base base riser MON RON wt % wt % wt % A 85 15 — 80.49 96.87 0.331.24 1.52 B 85 — 15 80.60 96.90 0.39 1.28 1.03

Therefore, the outlined invention is basically distinct from what istaught in the open literature, since it suggests the segregatedinjection of a feed from a thermal or physical separation process thatshows a higher contaminant content.

Besides, basing the difference between feeds on the nitrogen content orthe change in the riser temperature profile only are not sufficientcriteria so that a conversion rise can be observed.

Conversion rises to valuable products are observed as a result of acombination of conditions that include not only the difference innitrogen content of the mixed feed but also a higher contaminantcontent, such as asphaltenes, aromatics, polynuclear compounds andnickel, as reflected in the density of the more refractory feed tocracking, but also the suitable atomization temperature of this feed aswell as the dispersion degree of same.

Besides, it should be clear to the experts in the field that theversatility of the present cracking process makes that by varying theinjection location of the more refractory feed throughout the riserlength, it may be possible to alter as desired the light productsprofile directed to higher yields either in LPG or in gasoline.

1. A process for the fluid catalytic cracking of mixed feedstocks ofhydrocarbon feeds from different sources, in a riser reactor and in thepresence of a zeolitic catalyst, under cracking conditions and in theabsence of added hydrogen, for obtaining mainly light products such asLPG, said mixed feeds comprising feeds A and B, with feed B being morerefractory to cracking, wherein said process comprises the segregatedinjection of said feeds A and B in distinct riser locations, andwherein: a) feed B is in an amount of from 5% and 50% by mass based onthe total processed feed; b) the injection location of feed A sets thebase of the riser reactive section; d) feed B is injected in one or moreriser locations downstream the injection location of feed A and shows,in combination: i) higher coke selectivity relative to feed A; and ii)higher contaminant content, and where the injection conditions of feed Binvolve: i) injection location between 10% and 80% of the total lengthof the riser reactive section; ii) improved dispersion; and iii)injection temperature equal or higher to the injection temperature offeed A, the LPG resulting from such cracking process being recovered inhigher amount than that obtained if feeds A and B were injected both inthe base of the riser reactive section.
 2. A process according to claim1, wherein feed A is a heavy distillation gasoil (HVGO).
 3. A processaccording to claim 1, wherein feed B is produced by a thermal or by aphysical separation process.
 4. A process according to claim 3, whereinfeed B is produced by a pyrolysis, delayed coking and shale oilretorting process.
 5. A process according to claim 1, wherein thecontaminants of feed B comprise total nitrogen, nickel andpolyaromatics.
 6. A process according to claim 1, wherein the processconditions involve absence of overall sensible quenching effectresulting from feed B.
 7. A process according to claim 1, wherein feed Ais injected in a location of the base of the riser reactive section soas to have a longer contact time with the catalyst suspension, wherebythe conversion into valuable products is increased.
 8. A processaccording to claim 1, wherein the injection of feed B in the riseroccurs downstream of the injection location of feed A, in the sectioncomprised of from 25% and 50% of the riser reactive section.
 9. Aprocess according to claim 1, wherein the injection location of feed Bof lower crackability is defined aiming at obtaining the maximumpossible LPG production, and depends on the properties of the processedfeeds of different crackability, on the percentage of the feed of lowercrackability processed based on the overall feed flow rate and on theriser outlet reaction temperature.
 10. A process according to claim 1,wherein the best location injection for feed B of lower crackability isthat, which provides the ideal operation conditions for maximizing LPGyield in the riser section comprised between the two feed injections,while allowing the minimum residence time required for feed B of lowercrackability to undergo the desired conversion into lighter products,including LPG.
 11. A process according to claim 1, wherein the overallcatalyst circulation rate is kept nearly constant during the cracking offeeds A and B.
 12. A process according to claim 1, wherein thetemperature rise in the riser section between the base of the reactivesection and the downstream riser injection location causes in saidsection a huge feed conversion, so as to favor the yield in the sum ofLPG and gasoline, by weight.
 13. A process according to claim 1, whereinin the section between the downstream injection location and the risertop, feed B undergoes catalytic cracking reactions without significantlyincreasing the coke content deposited on the catalyst.
 14. A processaccording to claim 1, wherein the place of the one or more downstreamlocations should be selected so that the lower contact time iscompensated by the optimization of the dispersion condition of feed B.15. A process according to claim 1, wherein the same feed B is injectedin more than one riser location.
 16. A process according to claim 1,wherein different feeds B and C are injected in more than one riserlocation.
 17. A process according to claim 1, wherein the temperaturelevels of the segregated portion of feed B are equal or higher thanthose of feed A injected in the base of the riser reactive section. 18.A process according to claim 1, wherein the injection of feeds A and Bof different sources in the base of the riser reactive section and inthe downstream riser location is carried out simultaneously.
 19. Aprocess according to claim 1, wherein the residence time of feed A inthe riser submitted to the catalytic cracking reactions, measuredbetween the injections of feed A and feed B, is in the range of from 0.5and 2 seconds.
 20. A process according to claim 1, wherein thetemperature rise in the mixing region between feed A and the regeneratedcatalyst is of from 10° C. to 50° C., provided by the injection of feedB in a riser location downstream of the injection location of feed A,and is in the range of from 520° C. to 650° C.
 21. A process accordingto claim 1, wherein the maximum temperature of feed B is 430° C.
 22. Aprocess according to claim 1, wherein the riser outlet reactiontemperature is in the range of from 520° C. to 590° C.
 23. A processaccording to claim 1, wherein the control system for the injection offeed B in the riser is completely independent of the variables of theFCC converter.
 24. A process according to claim 1, wherein alternativelythe control system for the injection of feed B in the riser is afunction of the desired mixing temperature in the contact region of feedA with the regenerated catalyst.
 25. A process according to claim 1,wherein alternatively the control system for the injection of feed B inthe riser is a function of the LPG yield.
 26. A process according toclaim 1, wherein alternatively the control system for the injection offeed B in the riser is a function of any other variable which is desiredto control and for this aim, any control logic may be used.
 27. Aprocess according to claim 1, wherein the flow of the reactive catalystto oil mixture is upwards.
 28. A process according to claim 1, whereinthe flow of the reactive catalyst to oil mixture is downwards.
 29. Aprocess according to claim 1, wherein feed A is uniformly injected inthe riser cross section by means of a plurality of highly efficientfeed-injectors.
 30. A process according to claim 1, wherein feed B isuniformly injected in the riser cross section by means of a plurality ofhighly efficient feed-injectors.
 31. A process according to claim 1,wherein the catalyst comprises a Y zeolite.
 32. A process according toclaim 1, wherein the catalyst comprises a ZSM-5 zeolite.
 33. A processaccording to claim 1, wherein the catalyst comprises a combination of Yand ZSM-5 zeolites in any amount.
 34. A process according to claims 31,32 and 33, wherein the zeolite catalysts comprise zeolites as additives.35. A process according to claims 31, 32 and 33, wherein the zeolitecatalysts comprise one zeolite as additive and the other oneincorporated to the FCC catalyst.
 36. A process according to claim 1,wherein the improved LPG yield results from the following conditionsbeing obeyed: i) the lower the crackability of feed B, the higher thetime required for same to attain acceptable conversion levels; ii) thehigher the percentage of feed B based on the total processed feed, thehigher the severity imposed to the cracking of feed A; iii) the fartherthe injection location of feed B relative to the injection of feed A,the higher the time during which feed A will be submitted to the moresevere cracking conditions that favor LPG yield; iv) the higher theoutlet riser reaction temperature, the higher will be the temperature atwhich feed A will be submitted to catalytic cracking.